The present invention concerns more precisely a method implemented by a computer for simulating fluid flows in a liquid hydrocarbon (i.e. oil) bearing reservoir, in particular when undergoing surfactant flooding to improve the final oil recovery.
The method uses a model of said petroleum reservoir in which the fluid in place can split in a plurality of physical phases, specifically a gas phase, an oil phase, a water phase and a microemulsion phase. In turn, each physical phase can comprise a plurality of components, the component list comprising at least water, a hydrocarbon, and a surfactant component. Often, a polymer component and a salt component are considered as well.
Determining the composition of a physical phase is determining at least a concentration and a quantity of each component in said physical phase.
The method usually includes a flash step for calculating the equilibrium of all the component compositions in each physical phase resulting from the phase split of a given feed. The flash step is used in particular to introduce a new phase in the reservoir model where and when needed during the simulation. The method also includes the construction of thermodynamic equilibrium constraints to be coupled to the flow (or transport) equations, to ensure that all the physical phases introduced in the simulation by the flash step remain in equilibrium at all time steps during the simulation.
The document US 2011/246164 discloses such a method for surfactant flooding simulation, that has the advantage of determining the relative permeability of the physical phases in such a way as to maintain physical continuity when and where the phase-state changes. The model takes into account a water phase, an oil phase, and a microemulsion phase, and transport is treated fully implicitly.
However, such method can take into account neither a gas phase, nor a plurality of hydrocarbon components inside the oil and microemulsion phases.